This invention relates to an implantable, inflatable dual chamber shape retention tissue expander having a resilient annular base and a generally hemispherical shape after inflation which is used to form a generally hemispherical pocket beneath the tissue to be expanded to, for example, provide an appropriately shaped pocket for the receipt of an implantable mammary prosthesis and to a method for using such a tissue expander.
Various types of human tissue expanders are commercially available: SILASTIC.RTM. Percutaneous Skin Expander from Dow Corning Wright, Arlington, Tenn. 38002; the RADOVAN.TM. Subcutaneous Tissue Expander from Heyer-Schulte Corporation, Goleta, Calif. 93017 which is described in U.S. Pat. No. 4,217,889 to Radovan, et al. (issued Aug. 19, 1980) and the CUI Skin Expander from Cox-Uphoff International, Santa Barbara, Calif. 93103. These tissue expanders are implanted and filled percutaneously (usually with an isotonic saline solution) gradually over an extended time period for use in post mastectomy reconstruction techniques to prepare a pocket for receipt of an implantable mammary prosthesis, for use in the correction of hypoplasia or to generate additional tissue for use in scar revision procedures. Austad, in U.S. Pat. No. 4,157,085 (issued June 5, 1979), teaches an osmotically expandable tissue expander which does not require percutaneous inflation.
A problem inherent in prior art tissue expanders is that the tissue overlying the implanted tissue expander resists stretching as the tissue expander is inflated which causes the tissue expander to be forced into the shape of a sphere as it is inflated. The Radovan, et al, Patent teaches that the tissue expander must have a base which is inflexible or stiffly flexible to prevent possible damage to underlying tissue from pressure exerted by the tissue expander as it is inflated and also to control the shape of the skin enlargement obtained upon inflation. If the base is flexible, the base can curl on inflation. A pocket having the desired shape is more difficult to obtain when such curling occurs.
Rapid inflation can result in tissue necrosis, so gradual inflation over an extended period of time is the preferred practice. A capsule of fibrous contractile tissue can form around the tissue expander over the period of time during which the tissue expander is being gradually inflated, again tending to force the tissue expander into a spherical shape which results in a spherical pocket. A hemispherical pocket is preferred for post mastectomy reconstruction since the tissue expander is removed and replaced, for example, by a silicone gel-filled, silicone elastomer mammary prosthesis which has a generally hemispherical shape to replace the breast removed during the mastectomy procedure.
One example of an implantable mammary prosthesis is the SILASTIC.RTM. II Mammary Implant H.P. sold by Dow Corning Wright. Another example is the implant described in my U.S. Pat. No. 4,205,401 (issued June 3, 1980) entitled "Mammary Prosthesis Which Resists Capsular Contracture". The prosthesis described in my '401 patent is a sac which is filled with a filler material such as a silicone gel and further contains a restraining means for resisting the tendency for surrounding tissue to form the prosthesis into the undesirable shape of a sphere after implantation. This device is intended for long-term implantation into an existing pocket beneath the skin although the prosthesis can be filled with gel or other filler material after it is inserted into a pocket beneath the skin to reduce the size of the incision needed to implant the prosthesis. This prosthesis is not filled to its capacity, but is only filled with a sufficient amount of filler material to give the prosthesis a low profile shape and to give it a pliant responsive nature over its broad surfaces. The restraining means within the sac can be an annular ring filled with a filler material such as silicone gel to render it reactive to tissue pressure and to resist the tendency of surrounding tissue to form the prosthesis into a sphere.